Isomerization process



Patented Dec. 1S, 2%5

zsamss ISOMERIZATION rao'cnss Stephen F. Perry, Roselle, N. 1., assignorto Standard Oil Development Company, a corporation of Delaware NoDrawing. Application September is, 1942,

, serial No. 45s.:

'lclaims.

The present invention is concerned with the isomerization of straightchain or normal parafiins containing at least four carbon atoms permolecule to produce the corresponding iso or branched chain parafiins bymeans of catalysts such as those of the Friedel-Crafts issue. either inliquid or vapor phase and in the presence of promotional amounts ofhalogen-containing promoters such as, for example, hydrogen chloride,hydrogen bromide, chlorine, bromine, carbon tetrachloride, chloroform,the lower alkyl halides such as methyl, ethyl, propyl and butylchlorides and bromides. Aluminum chloride is the most commonly employedcatalyst, although the' bromide may also be employed.

The isomerization process as above described has been carried out bothin liquid and in vapor phase and aluminum chloride, either in granularor finely divided form or on porous carriers, has been the chiefcatalyst used; The carriers may be any number of different types such asactivated clays, bauxite, Porocel, alumina gel, activated carbon,activated alumina, silica gel and the like. The present invention isdirected to an improvement in such isomerlzation processes. Moreparticularly, the invention relates to a continuous vapor phaseisomerization process in which butane or pentane is passed in vaporphase at elevated temperatures and pressures through a bed of aluminumchloride sorbed in a partially dehydrated bauxite such as Porocel. thereaction bein bon disulfide, mercaptans and the like do remain in thefeed stocks which otherwise would be suitable for direct processing inan isomerization unit.

It has been discovered, however, that in the absence of expedients suchas those embodied in the present invention when these feed stocks whichhave been previously treated to remove the bulk .of the sulfurimpurities, but which do desirable because of numerous plant shutdownsdue to the formation of solid deposits in the various lines, valves,plates, etc., of the system. The fouling and plugging of these linesfrequently necessitates the complete shutdown of the system andlaborious and expensive cleaning of the carried out in the presence ofsmall amounts of hydrogen chloride. Such a process works very well andgives good yields of isobutane or isopentane, as the case might be,where the feed stocks are relatively pure hydrocarbons predominating instraight chain constituents to be isomerized, but oftentimes,particularly in refining operations, substantially pure parafiinic feedstocks are not to be found, and heretofore it has been found difiicultto utilize all types of pa raflnic feed stocks because of the presenceof numerous impurities. among which may be mentioned thesulfur-containing impurities. A number of the crudes which are refinedcontain small amounts of elemental sulfur, mercaptans, hydrogen sulfide,carbon disulnde and various other organic sulfur-containing' compounds.Conventional treating operations may be employed and are desirablyemployed to remove from refinery C4 or c. cuts substantial amounts ofthese sulfur type impurities, but such treatments do not completelyremove these impurities and hence even in thebesttreating operationssome very small amounts of one or more of hydrogen sulfide, elementalsulfur, carvarious plugged and fouled product lines. It has heretoforebeen thought that the fouling of the product recovery system was due tothe precipitation and deposits of aluminum chloride, but in the recentlyimproved, vapor phase operation the loss of aluminum chloride from thereaction catalyst mass ordinarily does not exceed 0.003 weight per centof aluminum chloride, which is well below the determined solubility ofaluminum chloride in liquefied iso or normal butane in the temperaturerange employed. But in spite of this, when running with a feed stockcontaining small amoimts of sulfur type impurities, fouling and plugginlof the lines eventually occurs. After careful investigation it wasdiscovered that the deposited material was not aluminum chloride but wasin fact a complex of aluminum chloride with hydrogen sulfide. Thismaterial has an extremely low solubility in liquid normal or iso butaneand is formed by the contacting of very small amounts of hydrogensulfide with aluminum chloride. This formationv was observed even infeed stocks which contained as little as 96 grains of hydrogen sulfideper thousand cubic feed of parafiinic feed stock going to theisomerlzation unit, by reason of the fact that the hydrogen suliidebuilt up in the system because it was carried overhead with the hydrogenchloride promoter which was recycled to the isomerization unit afterpurities. It is a further object of the invention.

to-remove from the system hydrogen sulfide at convenientselectedlocations therein so as to prevent plugging and fouling of valves. pies, plates and the like atsinaccessible places in the system but to formcomplexes at these desirable locations so that they may be removedreadfly as solid complexes, without the attendant removal of largeamounts of HCl. Other objects will be apparent upon a fullerunderstanding of the invention hereinafter more completely described.

Briefly, these objects are accomplished by the insertion into therecycle system of an isomerization unit of a chamber charged withaluminum chloride or with metallic copper in a suitable comminutedstate. The overhead from the stripping oi' the reacted mixture. which iscomposed ehiefiy of hydrogen chloride but contains appreciable amountsof hydrogen sulfide, is first passed through this chamber wherein thehydrogen sulfide is reacted with the substances contained therein sothat either a hydrogen chloride substantially completely free oihydrogen sulfide or a hydrogen chloride containing a reiuced amount ofhydrogen sulfide is recycled from the stripping operation to theisomerization catalyst zone during the isomerization reaction. it is notnecessary to employ solely aluminum chloride or metallic coppen. Anysubstance known to selectively react with hydrogen sulfide to form aninsoluble reaction product therewith under these conditions may belikewise employed. However. these two substances have been found bequite satisfactory in accomplishing the desired objects of theinvention. By so locating the unit for the removal or hydrogen sulfidethe net result is to get the hydrogen sulfide removed from the system ata readily accessible spot in preference to the formation or an insolublecomplex or sulfide in inaccessible spots in the system such as in aproduct cooler, in a stripping tower, or in lines or valves, connectingsuch pieces of equipment. Generally it is desirable to maintain a largebody or bed of aluminum chloride or copper burnings, balls, pelletts,grindings, powder or the like through which the stripper gases pass, andif aluminum chloride is used it is likewise desirable to maintain thehydrogen sulfide removal means at a somewhat lower temperature than anyexisting in the product condenser or lines since it has been found thatthe hydrogen sulfide is more completeu removed by means of aluminumchloride complex formation therewith at lower tem peraturm.

Inpiaee ofusingfre'shsluminumchloridefor the removal of hydrogensulfide, spent or partially spent isomerisation catalyst masses ofaluchloride sorbed in. Porocel type carrier maybe employedin the removalothydrogensulfide i'rom thestrlpped gas either with or without theaddition or fresh quantities of alumininnchloridetothespentisomerisationcatalystmassrBytroatingthehydrogenchloriderecyclestream toremovethehydrogen-sulfidetherefroi'n,still another advantage accruesin the overallefiicleneyoitheprocembyreasonoithefactthat "Dhydrogensulfidecyclestreamisiargreaterthanitspartialpressurointheproducteluentstreamwherebutanespartialpressureinthereor other similar p'arafiins act as dlluents to thehydrogen sulfide and hydrogen chloride. The hydrogen sulfideis thereforemore completely and conveniently removed from the system than :could beaccomplished by treating the iced or product stream. In the operation ofthe hydrogen sulfide removal step it is only necessary to maintainconditions such as to take out enough hydrogen sulfide to maintain asubstantially constant yet exceedingly low partial pressure ofhyformation or reactant formation such as copper sulfide in the hydrogensulfide removal step. Several of the heretofore mentioned expedientstend to accomplish this overall result.

In order to more fully understand the precise nature of the invention itmight be pointed out that complexes of the hydrogen sulfide withaluminum chloride are known to exist in crystalline form and apparentlythey are similar in nature to the crystalline hydrates and havecompositions ranging from AlaClaOJHaS up to as high as AlzClaJHzS.Usually the proportion of hydrogen sulfide contained is greater at lowertemperatures V and at higher partial pressures of hydrogen sulfide andthis tends to give a preferential formation of AlChJ-hS complex in therecycle stream coming from the stripping tower back to the isomerizationunit, particularly where the lower temperature is maintained in thisremoval drum. Once the complex is formed in the hydrogen sulfide removalstep the AlCls is no longer useful (until after regeneration) and it isnecessary for free aluminum chloride to combine with further quantitiesof hydrogen sulfide in order'to further remove the hydrogen sulfide fromthe recycle stream. it a particular batch of aluminum chloride becomesfully chemically .reacted so that substantially all of it is in the formof hydrogen sulfide complex the mass may be regenerated simply byreleasing the pressure, raising the temperature slightly. but at anyevent not higher than 200 F., and purging the hydrogen sulfide from thesystem; in a continuous operation the hydrogen sulfide absorber would beby-passed momentarily while this purging oi the aluminum chloride masswas being carried out.

The invention is not limited to the use of any particular or specifictype of feed stock except that the feed stock should predominate innormal parading of at least four carbon atoms per molecule, andpreferably less than nine carbon atoms per molecule for best results.Thus, for example, normal butane. normal pentane, normal heptane, normalhexane, or mixtures or two or more of these, field butane. casingheadgasoline, straight run naphthas and the like, are all suitable feedstocksior use in connection with the present invention. As previouslypointed out, however, these feed stocks in order to fully advantage ofthe invention will contain -theprocesshasbeens total sulfur content,either as suliur or in organic combination, should of course be inminimum but uccessiuliy' operated with concentration; of total sulfur ofaboutgrains per thousand cubic feet or gaseous feed stock,

order to substantially dehydrate it and free it I which may beconsidered typical of feed stocks which are normally available forisomerization. It is probable that considerably higher concentrationscould also be handled successfully.

The hydrogen chloride or other suitable hydrogen halide promoter isemployed in amounts ranging between about 1% and about 22%, preferablybetween about 5% and about 10%, all percentages being by weight based onthe feed, and the aluminum chloride is present in the reaction zone,particularly for vapor phase isomerization reactions, impregnated orsorbed on a carrier, the aluminum chloride constituting between about 6and about 18 weight per cent of the carrier. preferably between about 8and about 12'weight per cent of the carrier. This carrier should containonly tenaciously absorbed aluminum chloride and the carrier shouldpreferably have been dried previously at a temperatur considerablyhigher than the high'est temperature to be encountered in theisomerization reaction 50 that it is substantially dehydrated and'nofurther quantities of free water will be given off during theisomerization reaction. The impregnation of the carrier with thealuminum chloride may b in liquid phase as by the use of a solvent. oraluminum chloride vapors may be passed into the carrier mass undertemperatures around that to be employed in the isomerization reaction,and then the mass may be purged by heating the same up to from 100 to200 F. higher than that to be encountered in the reaction zone whilepassing through an inert gas to remove any loosely held aluminumchloride particles or vapors.

The temperature under which the isomerization reaction is carried out inthe vapor phase is more or less well known. However, in general, itranges between about 200 F. and 375 F. or as high as 400 F. depending onthe particular feed stock employed. In the case of normal butane. thepreferred temperature range is between 250 F. and 325 F. The pressuresare usually adjusted so that they range between 100 and 450 pounds persquare inch. For butane isomerization, these pressures are preferablybetween 150 and 300 pounds per square inch. The temperature maintainedin the hydrogen sulfide removal unit when using aluminum cholride isusually between F. and 75 F. lower than the lowest temperaturemaintained in the isomerization unit and product efliuent stream beforestripping. Where metallic copper is used as the removal agent forhydrogen sulfide in th hydrogen halide recycle stream, room temperatureor slightly higher is satisfactory, although temperatures of 40-50 F.were employed for the hydrogen sulfide removal in a specific run whereinthe metallic copper was maintained under a pressure of about 250 poundsper square inch with the stripper gas containing about 15% hydrogenchloride. The throughput of normal paraffinic feed stock through theisomerization unit may vary considerably, but for butane isomerizationit ranges .between about 0.5- and about 2 liquid volumes of feed stockper volume of catalyst per hour.

. Example A specific example of an operation embodying this invention isas follows:

A cylindrical vertical reaction chamber of ap-;

proximately 3 inches in diameter was substantially filled with acatalyst composition made up as follows: Eleven pounds of Porocelwhich'had been heated to about 1000 F. for about hours in from anyreadily separable water was charged on top of about 1.5 lbs. of granularaluminum chloride in this reaction chamber. The mass was then heated toabout 300 F. and a stream of butane was passed upwardly therethrough atatmospheric pressure for about 24 hours. The reaction chamber was thenclosed to the atmosphere and a feed stock containing about 6.6 volumeper cent isobutane, about 93.1 volume per cent normal butane and about0.3 volume per cent of C5 and heavier parafllns, and which alsocontained, byanalysis, 96 grains of sulfur and' sulfur-containingimpurities per thousand cubic feet of gas, was admixed with dry hydrogenchloride in an amount of about 6 weight per cent of hydrogen chloridebased on the feed mixture and this mixture was then passed upwardlythrough the catalyst mass under apressure of about 200 lbs/sq. in. andat a temperature of between about 250 F. and about 300 F. at athroughput of about 1 liquid volume of butane feed per volume ofcatalyst per hour.

and was then passed to a stripping tower having a bottom temperature ofbetween about 200 F. and about 215 F. and a top temperature of betweenabout F. and about the entire tower being maintained under a pressure.about 250 lbs/sq. in. At the top of this tower a refrigerated condenserwas inserted and the hydrogen 40 as copper sulfide. In fact. as long asany appreciable amounts of unreacted surface of copper remained, thehydrogen sulfide concentration was kept sumciently low so thatprecipitation of AlCla-HzS complexes in the isomerization unit properwas avoided. The process as above described was carried out continuouslyover a period of- 650 hours and during the operation the yield ofisobutane ranged between about 30% and' 50% based on the normal butanecharged, with an average yield of over 40%, with about of the normalbutane that reacted being isomerized to isobutane.

In the specification and annexed claims where mention is made of sulfurtype impurities or some similar expression is used, it isintendedthatthis expression be broad :enough.-to'. cover-.not onlytheresence of elementali sulfur and hydrogensulfide but also the presenceof other'naturally occurring organic sulfur compounds such asmercaptans, disulfides, thioethers and the like, either as present infeeds from natural sources or present as prepared synthetically duringthe various treating operations and from which \suitable feed stocks forisomerization units originate in refinery operations. These organicsulfur compounds tend to be broken up by the isomerization catalyst,forming hydrogen sulfide.

Having th'us fully described and illustrated the character of theinvention, what is desired to be secured by Letters Patent is:

1. A process of isomerizing normal paraffin which comprises passing afeed stock predominantly composed of normal paramn containin four carbonatoms per molecule and containing small amounts of sulfur-containingimpurities in The eiiiuent was withdrawn from the upper portion of thereaction chamber contactwlthaluminumchlorideandinthepresconstituentsboiling below the boiling point of the normal parafiln feed, contactinsaid gaseous mixture with aluminum chloride to at least partially removethe sulfur-containing impurities as insoluble solid complexes with thealuminum chloride, and continuously returning the hydro- Ien'chloride sotreated to the isomerization reaction zone containing the aluminumchloride isomerization catalystandieedstock.

2. A process of isomerizing normal parafiins which comprises passing afeed stock predominantly composed of normal paraiiin containing fourcarbon atoms per molecule and containing small amounts ofsulfur-containing impurities in contact with aluminum chloride and inthe presence of promotional-amounts of hydrogen chloride, underisomerization reaction conditions, separating from the reacted mixture amixture oi hydrogen chloride together with small amounts oi normallysascous sulfur-containing constituents boiling below the boiling pointof the nor-' mal parafiln feed, contacting said gaseous mixture withmetallic copper to at least partially remove sulfur-containingimpurities as reaction products with metallic copper. and continuouslyreturning th hydrogen chloride so treated to the isomerization reactionzone containing the aluminum chloride isomerization catalyst and feedstock.

3. A process of normal parafiin having from four to nine carbon atomsper molecule which comprises continuously passing in vapor phase a feedstock predominantly composed of said normal promotional amounts ofhydrogen chloride under isomerization reaction conditions, separatingfrom the reacted mixture a mixture of hydrogen chloride together withsmall amounts of hydrogen sulfide contained in the reactor eii'iuent,conmixture with aluminum tacting the saidsaseous chloride at atemperature lower than any temperature maintained in the isomerizationzone and reacted mixture before separating the hydrogen sulfide andhydrogen chloride therefrom to at least remove the hydrogen sulfide aslain insoluble complex with the aluminum chlode. and continuouslyreturnin the hydrogen chloride so treated to the isomerization reactionzone containing the aluminum chloride isomerization catalyst and feedstock.

4. A process of isomcrizing normal paraiiin having from four to ninecarbon atoni's per molecule which comprises continuously small amountsof hydrogen sulfide in contact with aluminum chloride and in thepresence. or. promotional amounts of hydrogen chloride underisomerimtion reaction conditions,

with small amounts of hydrogen sulfidecontainedinthereactor efluent,contscting-the with metallic copper to at least sulfide from the ouslyreturning the hydrogen chloride so treated to the isomerization reactionzone containing the aluminum chloride isomerization catalyst and feedstock. Y

5. A process of continuously isomerizing normal butane in the vaporphase, said normal butane containing small amounts oi sulfur typeimpurities, which comprises passing said feed stock in admixtur withpromotional amounts or hydrogen chloride through a catalyst bed ofaluminum chloride sorbed in a porous carrier at a temperature of betweenabout 250 1'. and about 325' I"., under a pressure of between about 150and about'300 lbs./sq. in. at a throughput of between about 0.5- andabout 2 v/v/hr., continuously passing the reacted eiiluent to a strippng operation wherein a mixture comprising substantially hydrogenchloride, hydrocarbons lighter than butane. and hydrogen sulfidcontained in the reactor eiliuent.is removed overhead at a temperatureof between about 40 1''. and aboutllO" 1''. while the normal butane andisobutane are removed from the bottom of the stripp ng tower for furtherprocessing, said tower being maintained under a pressure of about 250lbs/sq. 1a., continuously passing the overhead gases from the strippingoperation in contact with'aluminum chloride at a temperature from:0 F.to 1".4. 'lower than any temperature maintained in the L- cycling thehydrogen chloride gaseous mixture so treated back to the isomerizationreaction zone in admixture with fresh feed stock.

6. A process as in claim 5 wherein normal pentane replaces normal butaneas the'feedstock and wherein the reaction conditions are correlated togive isopentane as the predominant final product, the reactiontemperature being somewhat lower than 250' I".

"l. A process of continuously isomerizing normal butane .in the vaporphase, said normal butane containing small amounts of sulfur typeimpurities. which comprises passing said iced stock in admixture withpromotional amounts of. hydrogen chloride through a catalyst bed ofaluminum chloride sorbcd in a porous carrier at a temperature of betweenabout 250 F. and about 325' E, under a pressure of between about i50 andabout 300 lbs./sq. in. at a throughput of between about 0.5 and about 2'v/v/hr., continuously passing the reacted emuent to a strippingoperation wherein a mixture comprising substantially all of the hydrogenchloride and hydrosen sulfide contained in the reactor eiiiuent isremoved overhead at a temperature of between about 40' I". and about1''. while the normal butane and isobutane are removed from the bot-'tom of the stripping tower for further said tower being maintained undera pressure of about 250 lbs/sq. in., continuously passin the overheadgases from the stripping operation in contact with metallic copper, andcontinuously recycling the hydrogen chloride gaseous mixture so treatedback to the isomerization reaction zone in admixture with fresh feedstock.

STEPHEN l". PERRY.

